This invention relates to automatic alarm systms which are placed in window casings and the like and which, trip an alarm when the window is opened or the device is tampered with. Many types of alarm systems for windows and doors are known in the prior art.
U.S. Pat. No. 873,935 (Fawcett, 1907) discloses an alarm system for attachment to a window comprising a plurality of electrical contacts in circuit with each other and normally closed, a plurality of separable bars adapted to keep the contacts closed and to allow the contacts to spring apart when the window is manipulated, the bars being wedged between the contacts and the sash of the window.
U.S. Pat. No. 545,835 (Alexander, 1895) discloses a burglar alarm comprising a combination with a frame of circuit wires carried by the frame and a grating comprising tubes detachably connected with the frame, sockets carried by the frame, wires within the grating tubes, wires contained within the sockets, contact pins and plungers carried at opposite ends of the wires in the grating tubes, and contacts carried by the wires in the sockets and normally out of contact with each other, the latter wires being in contact with the circuit wires at their outer ends. When any one of the tubes of the grating is cut or broken, and the wire contained therein is severed, the circuit will be closed and an alarm sounded by reason of the spring forcing the plunger into contact with the contact plates.
U.S. Pat. No. 1,003,234 (Cline, 1911) discloses the combination of a frame adapted to conduct electricity, a main electric circuit mounted on the frame but normally insulated therefrom and being normally closed, a signal circuit, means for closing the signal circuit, an electromagnet in the main circuit whereby the means for closing is held open by the current passing through the main circuit, and means connecting the frame with the main circuit so as to cut out the signal circuit closing means in the main circuit when the frame and main circuit are manipulated so as to bring them into electrical connection. At each side of the window frame there is secured a vertically disposed casing open at its outer side. Tubes are extended at intervals horizontally through the screen frame through each of which a wire is stretched on leaf springs which bear against insulation within the casing. Bars are placed across the outer edge of the casing at points opposite the ends of said tubes. Next the lower end of the window or screen frame contact posts are secured to and insulated from the inner walls of the casing, so that when the frame is in its lowered position said contact posts will engage the contact springs secured to the insulating blocks in the sides of the window casing. Said contact posts and the springs at the ends of the tubes are alternately connected by wires so as to form a circuit running from the spring on one side, through a contact post, a wire, a spring and a wire to the other side of the window or screen frame and thence up to the wire above and back to the other side of the window or screen frame until the circuit reaches the spring at the other side of the window frame. In the circuit there is a voltage-reducing means such as a resistance coil. The tubes are in electrical communication with the metal casings and a contact spring that is secured beside the spring at one side of the window screen frame, and is mounted like the spring beside it, and the upper end of the spring engages a contact post that is in electrical communication with the casing so that all of the tubes and the two casings and the post and the spring are in electrical communication with each other.
If a burglar should undertake to enter through the screen window, he would bend one of the tubes. The tube at the bend would come in contact with the wire extending through it, and thus cause a shunt circuit or change of circuit. In that instance the circuit, instead of going out through the spring and wire, would pass out through the tube, the casing, the spring and wire to the battery. In that event, as soon as the current ceases passing through the magnet, the switch arm would drop down and close the bell circuit, causing the ringing of the bell.
U.S. Pat. No. 2,195,291 (Zukor, 1938) discloses a protection device for windows comprising a bracket mounted on the top of a window frame, a plurality of vertical flexible telescopic members mounted on the bracket and adapted to extend across the bottom of the frame, means for supporting the bar to swing slightly forwards and rearwards, means for locking the extended ends of the telescopic members to the bar, electric contacts to the front and rear of the bar, means for latching the bar to the contacts, an alarm, and a circuit for sounding the alarm when the bar and contact are connected.
U.S. Pat. No. 2,086,405 (Darden, 1937) describes a combined fire and burglar alarm utilizing control apparatus comprising a closed cabinet, a switch arm pivotally mounted in the cabinet and capable of occupying either one of two postions, a pair of circuit controlling contacts engaged by the arm when in one position, and a different pair of circuit controlling contacts engaged by the arm when in the other position, automatic means for swinging the arm away from the first pair of contacts and into engagement with the second pair, and means inaccessible from outside the cabinet for locking the arm in engagement with the second pair of contacts.
U.S. Pat. No. 3,797,005 (Schwartz, 1974) discloses apparatus for locking sliding doors including an alarm which will indicate the presence of an unauthorized person when the sliding door is being forced. The apparatus includes a telescoping bar which can be pivotally attached at one end to a sliding door with the remote end of the bar engaging a fixed structure. The remote end of the bar includes a trigger electrically connected to an alarm which is energized when the door is forced open a slight amount.
There is no teaching or suggestion in these prior art references of the electrical alarm of this invention of which the following is a specification.